Tooth enamel consists of tightly packed carbonated hydroxyapatite crystals which are organized into rods (prisms) running obliquely to one another in alternating rows. This extraordinary 3D architecture is established during enamel development as a result of the coordinated activity of cellular processes and organic matrix secretion. The present proposal focuses on the role of the unique C-domain of the major enamel matrix gene product, amelogenin, as it pertains to enamel structural organization. In previous studies, we have documented a significant increase in amelogenin C-domain proline and glutamine tandem repeats and prismatic enamel organization during the amphibian/reptile to mammal transition. In the present application, we are using this evolutionary biology approach to decipher the role of the amelogenin C-domain in the evolution of complex enamel structure. As a first step, we have generated frog amelogenin- overexpressing mouse models featuring grossly altered enamel mineral organization and lack of prism formation. Enamel thickness was further decreased and prisms were lacking when amel-overexpressors were crossed with amel null mice. In order to understand how specific domains of the amelogenin gene might affect alterations in enamel biomineralization during vertebrate evolution, we are now submitting a research plan to determine the effect of amelogenin C-domain evolution as it relates to enamel matrix organization, enamel crystal and prism formation. Our studies are designed to test the hypothesis that complex mammalian enamel architecture is a result of enamel matrix structure sophistication facilitated by amelogenin C-domain evolution. PUBLIC HEALTH RELEVANCE: The purpose of this research project is to identify key factors in tooth enamel formation. Tooth enamel in frog teeth is thin, little organized, and soft, while tooth enamel in mammals'features sophisticated organization and is thicker and harder than frog enamel. Here we are comparing the difference between frog and mouse enamel to identify key differences in enamel formation on a protein level. We are interested in the center portion of the major enamel protein, amelogenin. We believe that this center portion plays an important role in enamel formation and we will use a number of models to find out whether our thinking is accurate. Among those model systems will be experiments in which we will mix this protein with crystal growth solutions and experiments in which we manipulate the major gene in mice. We hope that one day our approach will lead to new ways of repairing human teeth.